For a considerable period of time, the vaporous emissions from the crankcase of internal combustion engines have been routed to the carburetor or air inlet of the internal combustion engine for disposal. Thus, this system prevents these vapors from being emitted to the atmosphere untreated. While such a system is beneficial to the environment, during certain periods of operation of the internal combustion engine and the associated vehicle, the routing of large quantities of vapor from the crankcase is detrimental to engine performance. Therefore, these systems have utilized a valving mechanism to control the routing of crankcase vapors to the intaking system of the engine. These systems utilize a PCV device or positive crankcase ventilation valve to control the flow of emissions from the crankcase to the inletting of the engine.
The PCV device or valve controls air flow to the engine air fuel inlet so as to restrict circulation of crankcase vapors, particularly during idle and to open the system more fully for flow of crankcase emissions during high speed operation. The PCV valve functions generally in accord with the pressure differential between the crankcase or the valve chamber of the engine and the intake manifold of the engine. During low engine speeds, it is desirable to reduce the flow from the crankcase to the intake manifold. It is also desirable to reduce air flow during certain transient conditions, such as acceleration. This prevents excessive leaning of the combustion mixture which could result in stalling or stumbling of the engine.
The typical PCV valve includes a housing with an inlet and an outlet and a flow chamber therebetween including a flow control passage just upstream of the outlet. An elongated plug-like valve is movable in the flow chamber and has one end which normally is seated against a valve at the inlet to greatly decrease entry of vapors to the device. A light spring normally holds the plug valve in the position against the valve seat. The other end of the plug valve is configured with a taper so that as the plug valve moves against the spring, this end progressively fills the flow control passage to regulate the flow of vapors from the crankcase to the intake manifold. During idle conditions, when the vacuum pressure is at a maximum in the intake manifold, the plug valve is moved against the spring so that the tapered end thereof substantially occupies a large area of the flow control passage thereby restricting passage of emissions to the intake manifold.
During normal mid-range speed of the internal combustion engine, substantially greater crankcase emission flow is tolerated by the engine than at idle or low speed. Consequently, PCV valves are designed to provide a substantially greater flow of crankcase emissions to the intake manifold of the engine under these conditions.